Routes for delivering pharmaceutical actives include delivering actives by intranasal, pulmonary, buccal, sublingual, transdermal, and rectal administration. These routes tend to be used for avoiding first-pass metabolism of drugs that are swallowed. “First past metabolism” refers to the arrangement and order of placement of the metabolizing enzymes within the body of a human, with respect to the path followed by substances that enter the gastrointestinal tract by swallowing, and are absorbed into the general blood circulation. Items swallowed by humans, including food, drink, and medicines, enter the stomach and from there flow into the intestine. Many of the chemicals associated with the food, drink, or medicine pass through the mucosal membranes in the gastrointestinal tract and into the blood in the mesenteric veins draining from the intestine. The blood flow from the mesenteric veins passes into the liver. Metabolizing enzymes in the mucosal membranes of the intestine and in the liver can chemically alter the nature of substances passing from the intestine, through the liver, and into the common blood circulation of the body. Since all swallowed medicines are subject to the metabolizing capacity of the intestinal mucosal membranes and the liver before entering the general blood circulation of the body, frequently only a small fraction of those substances go unmetabolized, and reach the general blood circulation
Avoiding first pass metabolism can increase the bioavailability, or blood concentrations of the administered compound. Metabolic formation of metabolites of the administered compound, however, can at the same time decrease. Where formation of metabolites from the first pass metabolism is desirable, avoiding the first pass metabolism is not preferred since it logically leads to lower amounts of the metabolite in the blood. Furthermore, the blood concentrations of the active substance can increase, leading to potential toxicity or side effects attributable to the active per se. Reducing the amount of active in the dose for avoiding toxicity, concomitantly decreases the circulating blood levels of the active metabolite. This results in loss of therapeutic affect and ultimately, benefit to the patient. In order to provide a medication that is effective and avoids unwanted side effects, the composition and its means of delivery must be modified.
Respiratory illnesses covers a broad range of ailments, including viral infections and allergic reaction to inhaled allergens. Viral infections in the upper respiratory tract of humans leads to illness usually referred to as colds, or influenza. Such an illness is quite common in the general population and can be the cause of significant discomfort and suffering. Allergen inhalation also negatively impacts a fair number in the population at the same or even at a greater degree than those having a viral infection.
There are no generally regarded effective and convenient methods for preventing viral infections or allergies. In the case of viral infections, the body's natural defense mechanisms fight the infection for a period of time normally ranging from 3 days to 2 weeks. This being the case, the most commonly employed medicines treat the uncomfortable, problematic symptoms of these respiratory ailments. These symptoms include stuffy and runny noses, soreness and inflammation in the nose and throat, fits of coughing, general aches in the body, fever, and headache. Of these symptoms, coughing in uncontrollable fits is considered by many to be the most problematic and uncomfortable. Coughing disrupts normal respiration, leading to increased headache and sore throat as well as loss of sleep to the sufferer and others living with the sufferer
The compositions used to treat the above mentioned symptoms generally fall into one of the following pharmacological classifications: antihistamines; decongestants; antitussives; expectorants; mucolytics; analgesics, antipyretic and anti-inflammatory agents. The compositions are manufactured in a number of product forms, the most common being liquid syrups and elixirs for swallowing, mouth drops and lozenges as well as inhalants and topical creams or lotions that release volatile agents that are inhaled through the nose into respiratory tract. The compositions are typically swallowed immediately, or slowly dissolved in the mouth. They typically contain actives such as guaifenesin, that aids the body in the removal of excess respiratory mucus or phlegm, diphenhydramine, that lessens the negative effects including coughing and other symptoms due to histamine produced in the body in response to the viral infection, and dextromethorphan, that acts within the part of the human brain controlling the coughing reflex. Among these actives, dextromethorphan is the most commonly used active in the world for relief of cough.
Dextromethorphan, by virtue of it's physicochemical, absorption, and bioavailability properties, is a very good candidate for increasing bioavailability via methods of administration other than swallowing. For example it has been reported in patents and pharmaceutical literature that substantial increases in bioavailability can be achieved using intranasal formulations; see H. Char et al, Nasal Delivery of 14-C Dextromethorphan in Rats, Journal of Pharmaceutical Sciences 81:750, 1992.
What has not been realized until now is that after careful and diligent research into pharmaceutic, therapeutic, and side effect properties of active compounds, compositions can be made to positively improve the therapeutic effect without increased side effects or toxicity.